Cirrus Logic CRD4297-1 AMR, Product Data Book

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DS242RD1B1 3
CRD4297-1 AMR
CrystalClear™ AC '97 AMR Audio Modem Riser Reference
CIRRUS LOGIC ADVANCED PRODUCT DATABOOK
alog mixer, a stereo ADC, a stereo DAC, and a con-
trol and digital audio stream interface to the AC ‘97
controller.
The CS4297 contains two distinct functional sec-
tions: digital and analog. The digital section in-
cludes the AC-link registers, power management
support, SYNC detection circuitry, and AC-link se-
rial port interface logic. The analog section in-
cludes the analog input multiplexer (mux), stereo
output mixer, mono output mixer, stereo ADCs,
stereo DACs, and analog volume controls. This
section contains the components for the various an-
alog audio connections, and the 24.576 MHz crys-
tal master clock. For more information refer to the
CS4297 Data Sheet [3]. The capacitors required for
the CS4297 and their placement are discussed in
the CS4297 Data Sheet [3]. Refer to the Grounding
and Layout section of the data sheet for the recom-
mended routing of the audio section.
Power Requirements
The CS4297 requires both a d3.3 V and an
5 V supply. The digital power is supplied
from the AMR bus. A voltage regulator is recom-
mended for the analog supply. A Motorola
MC78L05 regulates the AMR +12 V supply down
to provide a clean +5 V analog supply for the
CS4297. The MC78L05 regulator can provide ade-
quate current, which is enough for the CS4297 and
associated analog circuitry.
Analog I/O
The CS4297 has many analog inputs and outputs
that may or may not be used depending on the sys-
tem’s application. Unused inputs should be tied to
Vrefout (pin 28) or capacitively coupled via 0.1 µF
to the analog ground plane. The analog section con-
tains the components for a headphone amplifier.
The Modem Audio, CD In, Audio In, and Aux In
headers are also part of the Analog I/O section. The
header and its associated components may or may
not be necessary depending on the audio inputs im-
plemented.
Audio I/O
A full feature set of the CS4297’s analog I/O and
digital out is represented on the reference design
card through internal and external connectors:
• Line Out
• Headphone Out
• Line In
• Mic In
• CD Audio In
• Aux In
• Video In
• Modem Audio connection
• Optical Digital Out
Four external 1/8" jacks, one external TOS-LINK
jack, and four internal header connections are used
for analog and digital inputs and outputs.
Line Out
The output of the CS4297 is capable of driving im-
pedances greater than 10 k
Ω
with a maximum out-
put voltage of 1 Vrms. The Line Out connection is
made via an external 1/8" jack.
• Maximum output level: 1 Vrms
Headphone Out
An external 1/8" jack provided for a headphone
connection. This output is driven by an amplifier
for low impedance loads such as 32
Ω
headphones.
• Maximum output level: 2.0 Vrms (no load);
1.5 Vrms (32
Ω
load)
• Maximum output power: 70 mW/channel
(32
Ω
load)